The dependency of the working load on different set-up or state parameters of cranes is usually shown in the form of so-called working load tables. The safe working load is shown in these, for example, in dependence on the parameters of radius and boom length. With larger radii and boom lengths, lower values result for the safe working load than with values lower in comparison with them. Working load tables with other parameters which have an influence on the safe working load are naturally also conceivable.
Cranes known today are operated such that the parameters are changed so much until the safe working load corresponds to the actual working load. As soon as this limit value has been reached, a further parameter change is suppressed, with the braking of the corresponding crane movement or of the movement of a crane component taking place abruptly. This has the result, on the one hand, that the load starts to swing and, on the other hand, that the drive components and the steel construction are exposed to substantial loads due to the abrupt stopping of the movement.
It is the object of the present disclosure to further develop a method of operating a crane such that the loads on the drive components and on the steel construction in the operation of the crane are reduced and the swinging of any load is prevented or is likewise reduced.
This object is solved by a crane whose safe working load depends on one or more changeable parameters, wherein the change of at least one of the parameters is made such that the speed of the parameter change is reduced continuously or step-wise before a parameter value is reached at which the safe working load corresponds to the actual working load. No abrupt or jolting stopping from a full adjustment speed therefore takes place, but a continuous or step-wise braking, i.e. the speed of the movement of the crane or of the crane component is reduced continuously or step-wise. This brings along the advantage that the swinging of any load can be prevented or at least reduced with respect to previously known methods and that the components of the crane such as the drive components or bearing components such as the steel construction may be less strained.
The reduction can take place continuously or also step-wise. The reduction in the speed can e.g. take place such that it is reduced on or before the reaching of the coincidence between the safe and the actual working load from a value reduced with respect to the other change speed in a stepped manner to zero or that the value of zero is achieved by a continuous reduction of the speed.
The method in accordance with the present disclosure can be used when the actual working load is zero or greater than zero. The parameters of the crane, such as the boom length, can also not be varied as desired without a working load. At the margin of the working load tables, the value zero results for the safe working load. If the crane approaches this table margin with respect to its parameters of relevance here, provision is made in accordance with the present disclosure for this approach to take place with continuously reduced or step-wise reduced speed. A corresponding procedure results when the actual working load is larger than zero and the safe working load is changed by a parameter change.
The parameter(s) to which the method in accordance with the present disclosure is applied can be many, such as a parameter relating to a position of the crane or of a crane component.
The parameter can also be the boom length, the boom angle, the derrick ballast radius and/or the angle of rotation of the slewing platform. As stated, these are examples; other parameters are naturally also conceivable.
Provision can be made for the speed of the parameter change to be reduced continuously or step-wise starting when a difference between the actual and the safe working load falls below a given amount, i.e. over a specific residual path.
This difference can adopt a constant value or a value which depends on the actual and/or safe working load or its difference or the ratio of this difference to the actual and/or safe working load.
Provision can be made for the speed of the parameter change to be reduced such that the speed of the parameter change adopts the value zero, i.e. the parameter value is no longer changed or is reduced to a specific value when the safe working load corresponds to the actual working load or exceeds it slightly. In this connection, the speed of the parameter change can be reduced from a reduced speed to zero or to the specific value in a further step or the speed of the parameter change can be reduced such that the value zero or the specific value is reached continuously, e.g. in a linear or asymptotic manner.
It is particularly advantageous if the change of the parameter(s) is made such that the actual working load cannot exceed the safe working load.
The present disclosure furthermore relates to a crane having means which controls the crane in accordance with one or more of the various methods described herein. It can, for example, be a derrick crane or a mobile crane. Other crane types are also feasible.